1. Field of the Invention
The present invention relates to lubricating oils for the lubrication of gas fired engines and to the use of anti-oxidants to provide such oils with resistance to oxidation and nitration.
2. Related Art
Gas fired engines are typically 4-cycle engines having up to 16 cylinders similar to heavy duty diesel engines. The engines are used in the Oil and Gas industry to compress natural gas at the well heads and along pipelines as well as to generate local power. Due to the nature of this application, the engines fueled by natural gas often run continuously near full load conditions, shutting down only for maintenance or oil changes. Because the lubricant is subjected to a constant high temperature environment, the life of the lubricant is often limited by its oxidation stability. Moreover, because natural gas fired engines run with high emissions of nitrogen oxides (NOx), the lubricant life may also be limited by its nitration resistance. A longer term requirement is that the lubricant must also maintain cleanliness within the high temperature environment of the engine, especially for critical components such as the piston and the piston rings. Therefore, it is desirable for gas engine oils to have good cleanliness qualities while promoting long life through enhanced resistance to oxidation and nitration.
U.S. Pat. No. 6,642,191 is directed to a lubricating oil containing a particular phenolic antioxidant useful for natural gas fueled engines. The patent recites that the lubricating oil employs as base oil a Group II, Group III or Group IV base oil in combination with one or more of a hindered phenol of the general formula
wherein R is a C7 to C9 alkyl group. The lubricating oil can also contain dispersants, wear inhibitors and detergents. The Group II, III and IV base oils are recited as including base oils that may be derived from natural lubricating oils, synthetic lubricating oils and mixtures thereof, and include base oils is obtained by the isomerization of synthetic waxes and slack waxes, and PAO. Despite the fact that the patent teaches away from the use of excess quantities of the recited hindered phenol as well as away from the use of additional types of other hindered phenols or other antioxidants as their presence may reduce the synergistic effect obtained when the recited hindered phenol is used with a Group II, III or IV base oil, the patent recites that additional antioxidants may be present including a lengthy list of other hindered phenols and diphenyl amine type antioxidants including alkylated diphenylamine, phenyl alpha naphthylamine and alkylated alpha-naphthylamine.
U.S. Pat. No. 6,756,348 is directed to lubricating oils having enhanced resistance to oxidation, nitration and viscosity increase. The lubricating oil utilizes an antioxidant system comprising sulfurized isobutylene in combination with one or more of a hindered phenol. The hindered phenol can be butylated hydroxyl toluene, 3,5-di-t-butyl-4-hydroxy phenol propionate C7-C9 alkyl ester and mixtures thereof. Additional antioxidants can be present including other phenolic type anti oxidants as well as diphenylamine type antioxidants including alkylated diphenylamine, phenyl alpha-naphthyl amine and alkylated alpha naphthyl amine. In addition, organo molybdenum compounds such as sulfurized oxymolybdenum di-thiocarbamate may also be present. The base stocks include Group I, II, III, IV and V type base oils and include natural and synthetic stocks including PAO, isomerate of synthetic waxes or slack waxes. In the Examples only Group I or Group II base oils were employed.
U.S. 2004/0198615 is directed to a lubricating oil composition containing a Mannich product obtained by the reaction of an aldehyde, an amine and a di-secondary alkyl hindered phenol, and at least one additional additive selected from the group consisting of hydrocarbyl diphenylamines, sterically hindered phenols, metal hydrocarbyl dithiophosphates, molybdenum dithiocarbamates, sulfurized olefins and mixtures thereof. The oil of lubricating viscosity includes any natural or synthetic oil or mixtures thereof. Synthetic oils include polymerized or interpolymerized olefins, PAO, liquid esters, liquid esters of phosphorus containing acids, synthetic oils produced from Fischer-Tropsch reactions and hydroisomerized Fischer-Tropsch hydrocarbons and waxes. Antioxidants are recited as generally including hydrocarbyl diphenylamines, and sterically hindered phenols.
EP 1,265,976 is directed to a method for controlling soot induced viscosity increase in diesel engine lubricating oils by using a combination of additives which are an oil soluble trinuclear organo molybdenum compound and at least one other compound selected from a phenolic antioxidant and an aminic antioxidant. The base oils for the diesel engine lubricating oil include natural or synthetic lubricating oils having a kinematic viscosity at 100° C. of 3.5 to 25 mm2/s. The phenolic antioxidants are preferably hindered phenolic antioxidants and exemplified by a long list of the typical hindered phenolic antioxidants. Aminic antioxidants are described as diarylamines, aryl naphthylamines, alkyl derivatives of the diarylamines and of the aryl naphthylamines, including butyl phenyl α-naphthylamine, pentyl phenyl-α-naphthylamine, hexyl phenyl-α-naphthylamine, heptyl phenyl-α-naphthylamine.
U.S. Pat. No. 6,730,638 is to a lubricating oil formulation containing a lubricating oil base stock, a boron containing ashless dispersant, a molybdenum containing friction reducing agent, a metal type detergent and zinc dithiophosphate. Also present can be phenolic and aminic antioxidants and mixtures thereof. Table 1 describes formulations containing mixtures of phenolic and aminic antioxidants but does not identify the particular ones employed.
U.S. Pat. No. 6,153,564 is directed to lubricating oil compositions comprising a base stock having a kinematic viscosity at 100° C. of from 2 to 20 mm2/s, an oil soluble trinuclear organo-molybdenum compound and other additives which include antioxidants. Suitable antioxidants include copper-containing antioxidants, sulfur-containing antioxidants, aromatic amine-containing antioxidants and phenolic antioxidants. Numerous examples of each type are given. Among the many aminic-type antioxidants recited are naphthyl amines, diphenylamines including alkyl substituted diphenylamines.
U.S. Pat. No. 6,734,150 is directed to a lubricating oil composition comprising a base stock and an antioxidant comprising an oil soluble trinuclear organomolybdenum compound and at least one other compound selected from a phenolic antioxidant and an aminic antioxidant. The base oil has a kinematic viscosity at 100° C. of 2 to 20 mm2/s and includes Group II and Group III base stocks which may be a natural or synthetic lubricating oil. Phenolic antioxidants are preferably hindered phenolic antioxidants and are exemplified by a lengthy list while aminic antioxidants are generally identified as diarylamines, aryl naphthylamines and alkyl derivatives of the diarylamines and of the aryl naphthylamines. Preferred antioxidants are represented by the formula
wherein each of R4 and R5 is hydrogen or the same or different C1-C8 alkyl group. Included in a lengthy list of amines are recited various alkyl phenyl-α-naphthylamines.
See also U.S. Pat. Nos. 6,143,701; 6,010,987;
EP 0,860,495 is directed to a lubricating oil composition for gas engine heat pumps comprising a base oil and 0.5 to 10 wt % of a metal salicylate detergent having a total base number (TBN) of from 100 to 195 mg KOH/g; 0.1 to 10 wt % of at least one aminic antioxidant; 0.1 to 10 wt % at least one phenolic antioxidant and 1 to 10 wt % of a polyalkenylsuccinimide or a boron-containing poly alkenyl-succinimide. In a preferred embodiment the aminic antioxidant is composed of a dialkyl diphenylamine and a phenyl-α-naphthylamine. Base oils have kinematic viscosities at 100° C. of from 3.5 to 20 mm2/s. No limitation is placed on the base oil, which can be mineral oil or synthetic base oil. Mineral base oils can be oils available from lubricating oil refining steps of raw materials for lubricating oils such as solvent refining using phenol, furfural, N-methyl pyrollidone or the like, hydrofining and wax isomerization, light, medium or heavy neutral oil, bright stock and the like. Synthetic base oils include PAO, polybutenes, alkyl benzene, polyol esters, polyglycol esters, dibasic acid esters and the like. In Example 1, a hydrorefined oil was combined with calcium salicylate, phenyl-α-naphthylamine and dialkyl diphenylamine, a hindered phenol mixture, polyalkenylsuccinimide, ZDDP, moly DTC, ethylene-propylene copolymer, polymethacrylate, alkenyl succinic acid, benzotriazole and dimethyl polysiloxane. In subsequent examples the ingredients were either varied or selectively omitted. In all instances the base oil was a hydrorefined oil.
U.S. 2006/0014653 is directed to a low ash, high TBN engine oil comprising a base oil, a detergent package selected from one or more phenates, salicylates and sulfonates each independently having a TBN of from 30 to 350 mg KOH/g and at least 3.5 wt % of one or more antioxidants selected from aminic and phenolic antioxidants. Aminic antioxidants include alkylated diphenylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamines and alkylated α-naphthylamine. Many typical amines of each type are recited in a general disclosure. Phenolic antioxidants are also broadly described. Base oils can be conventional known mineral oils and synthetic. Base oils can be naphthenic base oils, PAO, dibasic acid esters, polyol esters, dewaxed waxy raffinate. Preferred base oils are mineral or synthetic oils which contain more than 80 wt %, preferably more than 90 wt % saturates, less than 1.0 wt %, preferably less than 0.1 wt % sulfur and have viscosity indexes of more than 80, preferably more than 120, and kinematic viscosities @100° C. ranging from 2 to 80 mm2/s.
The Examples employ a mixture of Group III base oils identified as XHVI-5.2 and XHVI-8.2 formulated with the phenolic antioxidant ((C7-C9 branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy benzene propanoic acid) Irganox L-135) and, in one instance the phenolic antioxidant used in combination with Irganox L-57 which is an alkylated diphenylamine.
U.S. 2005/0288194 teaches the preparation of an oligomeric phenolic detergent. Lubricating oils can be formulated comprising any mineral and/or synthetic base oil in combination with the oligomeric phenolic detergent. Base oils include oils derived from natural sources, mineral oil, synthetic oils such as PAO, alkyl benzenes, synthetic esters, Fischer-Tropsch hydrocarbons etc. Other additives can be present including dispersants, phenolic antioxidants, aminic antioxidants such as diphenylamines, alkylated diphenylamine, phenyl α-naphthylamine, alkylated α-naphthylamine, metal dithiocarbamates, anti-rust agents, demulsifiers, extreme pressure agents, friction modifiers, viscosity index improvers, pour point depressants, foam inhibitors, metallic detergents, etc.
In the Example of a formulated oil no aminic antioxidants were employed.
U.S. 2005/0209110 is directed to a lubricating oil containing sulfonates and phenates, a base oil of lubricating viscosity. Base oils include natural and/or synthetic oils, i.e., mineral oils, vegetable oils, petroleum oils, coal or shale oils, polymerized olefins, alkyl benzenes, esters of phosphorus-containing acids, Fischer-Tropsch derived oils, oils from the hydroisomerization of Fischer-Tropsch wax. Antioxidants can be present and include hindered phenols, diphenylamines, molybdenum dithiocarbamates, sulfurized olefins and mixtures thereof. In the Examples a mixture of Exxon™ 600N oil and Exxon™ 150 Bright stock was employed as base oil. None of the Examples appear to utilize any aminic antioxidant of any type.
U.S. 2004/0142827 is directed to a lubricating oil comprising a major amount of at least one Group II, III or IV base oil and a minor amount of 2-(4-hydroxy-3,5-di t-butyl benzyl thiol) acetate hindered phenol antioxidant useful as a natural gas engine oil. Base oils include natural or synthetic oils e.g., animal oils, vegetable oils, petroleum oils, mineral oils and oils derived from coal or shale, oils made by isomerization of synthetic wax or slack wax, hydrocrackate base stock, PAO, alkyl benzenes, poly phenyls, alkylated diphenyl ethers, alkylated diphenyl sulfides, alkylene oxide polymers, esters, polyol esters, phosphate esters, silicon-based oils. Additives include the particularly recited hindered phenol antioxidant, detergent, dispersant, and wear inhibitors. Other additives may also be present including additional antioxidants such as phenolic antioxidants and diphenylamine-type antioxidants which include alkylated diphenylamine, phenyl-α-naphthylamine and alkylated-α-naphthylamine. In the Examples Group I and Group II base stocks were utilized.
U.S. Pat. No. 5,726,133 is directed to a natural gas engine oil comprising an oil of lubricating viscosity which can be any natural or synthetic oil or mixture thereof including base stocks obtained by the isomerization of synthetic wax or slack wax, a detergent package and other additives including dispersants, antioxidants, antiwear agents, metal deactivators, antifoamants, pour point depressants and viscosity index improver, antioxidants may be phenolic or aminic or mixtures thereof. See also US 2005/0153851; U.S. Pat. Nos. 6,140,282; 6,191,081; 6,140,281.
U.S. Pat. No. 6,080,301 is directed to a premium synthetic lubricant base stock having at least 95% non-cyclic isoparaffins. The base stock is made by hydroisomerizing a Fischer-Tropsch wax. The base stock can be formulated into a lubricating oil by adding an effective amount of one or more performance additives including detergents, dispersants, antioxidants, antiwear additives, pour point dispersants, viscosity index improvers, friction modifiers, demulsifiers, antifoamants, corrosion inhibitors, seal swell control additives.